This is a proposal to study mechanisms by which parallel visual circuits are formed, transmitted and preserved in the retina. The PI has developed intracellular staining and quantitative tracer coupling analysis into techniques capable of exploring features of bipolar cell connectivity and gap junctional pathways not easily obtained in other ways. The PI will build on these advances by determining some of the synaptic partners of 2 poorly characterized bipolar cell subtypes and by using tracer coupling analysis to study the properties of 2 types of lateral gap junction in the cone bipolar pathway. Specific Aim 1: The degree of association between single stained bipolar cells and identified ganglion/amacrine cell processes will be quantified with confocal microscopy. Electron microscopy will be used to definitively establish contact between the most promising candidates. The results will define some new types of retinal circuit. The PI will test hypotheses that each bipolar cell contacts specific third-order neurons. Specific Aim 2: Additionally, the PI will examine the mechanisms by which the AII amacrine cell, a pivotal interneuron in mammalian scotopic vision, makes gap junctions with all ON cone bipolar cells, yet does not degrade spatial sensitivity or channel independence at photopic levels. The PI will quantitatively measures the coupling rates between AII amacrine cells and individual cone bipolar cell types to test the hypothesis that parallel bipolar cell circuits are independently regulated by multiple mechanisms. Specific Aim 3: Using methods developed to study other small cells, the PI has already observed tracer-coupling between rabbit clones. He will test the hypothesis that coupling is reduced under photopic conditions to maintain special acuity by closing gap junctions via dopamine and cAMP. He will further determine if coupling between neighboring cones is weighted preferentially to cones of the same type or is completely indiscriminate.